tools: add sample remote_bitbang sysfsgpio server

This adds a sample server that implements remote_bitbang protocol,
based on sysfsgpio interface driver.

Change-Id: I17633e91f819ab7b806606e1a1c38d5366ab4598
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/1403
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>